MR imaging and spectroscopy require spin order in the species to be studied. This order is most commonly imposed by the application of a magnetic field, but it may also arise from spin-polarized photons (e.g. hyperpolarized gas imaging) or from rotational symmetry considerations in hydrogen. As the H2 dimer approaches the moderately low temperature of tens of Kelvin in the presence of a paramagnetic relaxation site, the proton nuclei spontaneously order into the nuclear singlet state preferentially over the three triplet states. While this order cannot itself be imaged, it can be transferred to polarization of protons or heteronuclei through hydrogenation of a double bond. The resulting images of hyperpolarized 13C and other heteronuclei show great promise for angiography, quantitative perfusion measurements and molecular imaging applications.
Up to now, the determination of the para content of the hydrogen has been based either on NMR measurements or the principle that ortho- and parahydrogen have slightly different thermal conductivities. By measurement of the thermal conductivity and comparison with a reference gas, the para content of the hydrogen can be determined. However, this measuring technique is comparatively expensive and inaccurate. Thus, because of the increasing number of uses for hydrogen and other gasses with different spin states in the near future, a simpler and more inexpensive process for determining the specific nuclear symmetric state is needed.